Pressure monitor

ABSTRACT

The present invention is a pressure monitor for measuring the pressure in a liquid in catheter, comprising a light emitting device, a photosensitive device receiving the light from the light emitting device and transforming the light received into electric signals. The invention also includes a measuring zone. The light transmitted through the measuring zone varies in accordance with the pressure in the catheter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT/DK93/00122 filed Apr. 1,1993, filed under 35 USC 371.

The inventions relates to pressure monitors and to be more specific topressure monitors for measuring the pressure in a catheter.

From WO 90/07942 it is known that the overall correct function of aninfusion pump may be supervised by considering the course of thepressure in the outlet catheter during each pumping cycle. It isimportant that the actual pressure in the very catheter is measured andnot just the resistance a piston exerts against movement.

It is the object of the invention to provide a pressure monitormeasuring the pressure in the catheter directly.

This is obtained by a monitor comprising a light emitting device and alight measuring device placed opposite each other leaving a space forinsertion of a measuring zone of the catheter between these parts, thismeasuring zone lying downstream of a possible output valve of a pump,and a computer circuit transforming the signals from the light measuringpart into signals representative to the pressure.

The light source may be one or more cooperating surface light emittingdiodes jointly having a size corresponding to the size of the measuringzone.

Correspondingly, the photo sensitive device may be formed by one or morephoto cells working in parallel and jointly having a size correspondingto the size of the light emitting device.

The measuring zone may be a part of the catheter tubing or may be anappendix to the catheter, this appendix forming a manometer tube.

When the manometer tube solution is used, the light measuring device mayappropriately be a linear array of mutually independent photocells, thisarray having a length corresponding to the length of the branch tube.With this embodiment of the light measuring part it can be measured towhich extent the infusion liquid rises in the manometer tube.

Catheters for infusion pumps may have the shape of a tubing forming thecomplete flow path for the liquid to be infused from a reservoir. Thepumping function may be obtained by part of the catheter forming a partof a peristaltic pump or being provided with another sort of pumpingunit. In the last mentioned case, the manometer tube may be provided inthis pumping unit downstream of the outlet valve of this unit. Therebyit is possible to mould the pumping unit with the manometer tube toobtain a more precise manometer tube.

The invention also comprises a catheter provided with a branch tubeforming a manometer tube. This branch tube may appropriately be providednear a pump delivering an infusion liquid through the catheter, butdownstream in relation to the output valve function of this pump.

A catheter may comprise a pumping unit forming a part of this catheter,and the branch tune may be provided as a bore in this unit.

In the following the invention will be described with reference to thedrawing, wherein

FIG. 1 schematically shows a monitor comprising a light emitting partand a light measuring part with an interjacent measuring zone of acatheter,

FIG. 2 schematically shows a monitor as shown in FIG. 1 where themeasuring zone of the catheter is provided as an appendix to thecatheter,

FIG. 3 schematically shows a monitor measuring the level in a manometertube.

A pressure monitor for measuring the actual pressure in a catheter isshown schematically in FIG. 1. The monitor comprises a light source 1which may be a light emitting diode, LED, emitting its light from anelongated surface, a photo cell 2 for receiving light on a surface ofabout the same size and shape as the light diode. The LED and the photocell are placed opposite each other and spaced so far that room is madefor accommodating a measuring zone of a catheter 3.

It has appeared that the light transmission through the liquid filledcatheter varies with the internal pressure in the catheter, andconsequently an output signal reflecting the pressure variations in thecatheter may be obtained from the photo cell. The signal is lead to acalculating unit setting the zero point, when a new catheter isinserted. Advantage is taken of the fact that a measurement of theabsolute pressure is not needed, as the monitoring method stated in WO90/07942 only considers variations in the pressure from one pumpingcycle to the other.

Another embodiment of a pressure monitor is shown in FIG. 2. In thisembodiment, not the catheter 3 itself but an appendix 4 on this catheteris inserted between the light source 1 and the photo cell 2. Theappendix has the shape of a short tube, the bore of which communicateswith the clear of the catheter and is closed at the outer end of theappendix. Thereby a manometer tube is provided.

When the catheter is filled with liquid, some air will be trapped in themanometer tube, and a surface 5 separating air and liquid will appear inthe manometer tube. When the liquid in the catheter is set underpressure, this surface will be forced further up into the manometertube. When the manometer tube is placed between the light source 1 andthe photo cell 2, the light transmission will be influenced by thevarying position of the liquid surface 5, as the transmission propertiesof the liquid filled part of the manometer tube will be different fromthe transmission properties of the part filled with air.

FIG. 3 shows an embodiment of a monitor measuring the light transmissionperpendicular to a manometer tube. This monitor has a light source 1 asthe embodiments according to FIGS. 1 and 2, but instead of one photocell or more photocells operating in parallel it has an array of photocells 5, each supplying its own output signal. Thereby it is madepossible to read exactly the position of the liquid surface 5, as adistinct difference in transmission may be seen between the cells in thearray receiving light from the light source through the air filled partand the cells receiving the light through the liquid filled part of themanometer tube.

When the catheter is filled with unpressurized liquid, the position ofthe separating surface is noticed and further the end of the appendixmay be noticed, as a distinct difference in transmission is also seenbetween the part of the appendix having an air filled bore and the solidpart closing the outer end of the branch tube. Hereafter the position ofthe separating surface may be read with a precision depending on thenumber, size, and spacing of the photo cells 6 in the array. Hereby theabsolute pressure may be calculated by recognizing the law for confinedgasses.

To discriminate between the signals from the photo cells 6 in the array,an output from each cell must lead to the computer. Alternatively, acircuit may be provided in connection with the array to transform theoutput signal to a sequential signal.

The monitor is intended to be a part of an infusion pump frequentlyinfusing doses of liquid. During each infusion the course of thepressure in the catheter has to be monitored to supervise that the dosesare actually infused and no functional errors occur. Consequently, themonitor needs only be activated in connection with the frequent infusioncycles, and power may be saved by turning off the light source betweenthese cycles.

We claim:
 1. An apparatus for directly monitoring the pressure of aliquid in a catheter, the apparatus comprising:a light emitting device;a photo sensitive device spaced from said light emitting device; and acatheter having a light transmissible measuring zone, said measuringzone being disposed between said light emitting device and said photosensitive device; wherein said photo sensitive device receives lightfrom said light emitting device transmitted through said measuring zoneof said catheter, said photo sensitive device transforms the receivedlight into electric signals reflecting an amount of light transmittedthrough said measuring zone of said catheter.
 2. An apparatus accordingto claim 1, wherein the light emitting device comprises a number ofco-operating surface light emitting diodes jointly having a sizecorresponding to the measuring zone.
 3. An apparatus according to claim1, wherein the measuring zone is a part of a tubing constituting thecatheter.
 4. An apparatus according to claim 1, wherein the measuringzone is a branch tube to the catheter, which branch tube has a closedend.
 5. An apparatus according to claim 4, wherein the branch tube isprovided in a part of a pump provided as an integral part of thecatheter, the branch tube being provided downstream in relation to valvemeans in said part.
 6. An apparatus according to claim 1, wherein thephoto sensitive device comprises a number of co-operating photocellsworking in parallel and jointly having a size corresponding to a jointlight emitting surface presented by the emitting device.
 7. An apparatusaccording to claim 4, wherein the photo sensitive device is a lineararray of mutually independent photo cells.
 8. An apparatus according toclaim 4, wherein the branch tube is provided near a pump delivering aninfusion liquid through the catheter, but downstream in relation to anoutput of this pump.
 9. An apparatus according to claim 4, wherein thebranch tube is formed as a bore in a pumping unit forming a part of thecatheter.
 10. An apparatus according to claim 1, wherein the amount oflight transmitted through said measuring zone varies with an internalpressure in said catheter.